1. Field of the Invention
The present invention relates generally to a system for providing a consistent force between a nudger and documents fed from a stack. More particularly, the present invention is directed to a system for compensating for variability in a nudger normal force resulting from variations in the number of documents in the stack, the weight of the documents in the stack, and the friction forces between the stack of documents and the hopper floors and walls.
2. Description of Related Art
A variety of automated machines such as document sorters, mail sorters, copiers, page feeders, punch card readers, automatic teller machines and fax machines utilize document feeders to move documents within a machine. Documents in a machine are often stacked and automatically fed from the document stack. A nudger moves the documents a short distance from the leading edge guide to the nip formed by the feed wheel and the separator belt. In the process of successively feeding documents from the stack, a nudger applies a force to a first document, while a flag applies a force to a last document. The flag force is transmitted through the document stack to the nudger, and the nudger, in response, applies a reactionary force normal to the document stack. The nudger, therefore, applies a force which is not only the tangential force caused by the rotation of the nudger about a fixed shaft, but also the reactionary force of the nudger applied in a direction normal to the flag. Commonly known systems for applying the flag force are springs, weights attached to cables and pulleys, incline planes, and motor-driven flags.
A great variety of document friction conditions exist in various applications, such as check processing, mail sorters, punch card readers, automatic teller machines and fax machines. Documents moving against the hopper floor can produce different variations in friction forces. These friction forces generated from the movement of the document stack subtract from the flag force applied to the document stack, thus the force transmitted through the document stack to the nudger is less than the flag force and therefore causes changes in the reactionary force the nudger normally applies to the document stack. A feedback control is required between the flag and nudger to maintain a consistent nudger force that does not vary in response to conditions in the document stack. If the nudger force is too large, the nudger moves multiple documents through the nip, and thus cause multiple feeds. If the nudger force is too low, however, the nudger fails to move documents to the nip, thus the documents do not feed through the nip. There is a need to measure the normal force at the nudger, and depending on this measurement, adjust the flag force to produce a desired nudger force.